40 nw. E. DAVID. 
being fairly accurate.! “ But even supposing the Hawkesbury 
Sandstones were formed under terrestrial conditions, there must 
have been a subsequent depression. The sea came over their site, 
and covered them with the fine argillaceous sediment of the 
Wianamatta shales, as their enclosed fossil fishes indicate.” Then 
followed a slow and extensive upheaval during which the soft 
shales must have been greatly denuded. Afterwards succeeded 
the era when the great Nepean Fault commenced, and the country 
south (east—T.W.E.D.) began to sink, whilst perhaps that to the 
north (west—-T. W.E.D.) was upheaved to form the region of the 
Blue Mountains. At length, with the exception of comparatively 
small patches, the Wianamatta shales were completely peeled 
off the Blue Mountains. The action of rain, running waters, 
frosts, snows, wind, andsun * * * began to eat into the 
harder Hawkesbury Sandstone rock beneath. It was merely a 
question of time. The work is still going on, and the total results 
are visible in the grand and awe-inspiring views presented at the 
Weatherboard (Wentworth Falls—T. W.E.D.), in the Grose Valley 
and elsewhere. There we behold immense valleys scooped out to 
more than 2,000 feet, walled in by mural precipices with 800 or 
900 feet of sheer perpindicularity, over which streams of water fling 
themselves. to be lost in gauzy mist before reaching the bottom. 
* From our giddy point of vantage, the arboreal vegeta- 
tion below looks like velvet pile. * * * The rich yellow walls 
of sandstone precipices on which the sun is shining, gleam with 
almost dazzling brightness, whilst the corresponding walls of the 
other side of the valley are plunged in densest gloom. Out of, 
and oo the curving and widening valley we are gazing down 
catenins 
1 Our Island-Continent—A Naturalist’s Holiday in Australia. By 
Dr. J. E. Taylor, ¥.1.s., ¥.a.s., London, 1886, pp. 249 - 250. 
2 The fossil fauna of the Wianamatta Shales, as proved by the presence 
of dwarf types of Unio and by the character of the fish is indicative of 
lacustrine or lagoon, rather than of marine conditions. 
Memoirs, Geological Survey of New South Wales, Palwontology, No. I. 
Invertebrate Fauna of the Hawkesbury-Wianamatta Series, by RB. 
Etheridge, Junr. 
